The purpose of this grant proposal is to investigate the role of the glialneuronal relationship in the process of central nervous system (CNS) elemental and ionic homeo-stasis and the effects of anesthetic agents (pentobarbital, halothane, and morphine) on that process. It is widely believed that glial cells are important to some degree in regulation of CNS elemental, water, and ionic composition. Despite considerable efforts to understand how inorganic elements and ions are moved about the CNS and how cell water is maintained, the results in this area are far from conclusive. This lack of information is due to the problems associated with making such measurements and does not reflect the importance of this fundamental information. Electron microanalysis (EPMA) of frozen hydrated tissue sections is a relatively new technique which can provide, in conjunction with ion-selective microelectrode measurements, this basic information which was not previously available using existing techniques. EPMA of frozen hydrated sections of leech (Macrobdella decora) ganglion will be used to determine the concentrations of selected intracellular elements and water content of normal glial cells and neurons. Ion- selective microelectrode measurements will be used to determine the relationship between total elemental content (measured with EPMA) and elemental activity of Na, K and Cl. The effects of ionic changes in the extracellular fluid (including Na, K, Cl, Ca, Mg, H) will be studied as well as the effects of tonicity and putative neurotransmitters (5-hydroxytryptamine and gamaaminobutyric acid). Experiments are proposed to determine the kinetics of elemental distribution and the effects of anesthetic agents on that distribution. These later experiments are designed to test the hypothesis that anesthetic agents may act by interrupting the neuron-glial interrelationship. In these experiments, anesthetics may also act as pharmacological probes useful for studying the neuronal-glial interrelationship. The results of these studies should provide previously unobtainable, fundamental information of value for basic research in neurobiology necessary to develop a more comprehensive concept of the neuron-glial interaction and its importance to CNS function. In addition, the results of these studies may also provide a basis for understanding how anesthetics work at the cellular level.